A typical prior art tablet digitizer system has a tablet and a transducer/cursor in the form of a pen or a puck. As is well known, there are two operation modes for determining the position of a pointing device on the surface of a digitizer tablet. One is a relative mode, and the other is an absolute mode.
A mouse device operates in a relative mode. The computer sensing the inputs from a mouse recognizes only relative movements of the mouse in X and Y directions as it is slid over the surface on which it is resting. If the mouse is lifted and repositioned on the surface, no change in the signal to the computer will be detected. A common approach uses a sensing apparatus inside the mouse to develop a pair of changing signals corresponding to the longitudinal and transversal movements of the mouse.
In contrast, a cursor device (such as a pen or a puck) in a digitizer tablet system operates in an absolute mode. If a cursor device is lifted and moved to a new position on its supporting surface, its signal to a computer will change to reflect the new absolute position of the cursor device. Various methods have been used to determine the position of a cursor device on the surface of its supporting tablet. One common approach is electromagnetic field sensing.
Early transducer/cursors were connected to the tablet by means of a multi-conductor cable through which the position and button/pressure information are transferred virtually without any problem. As cordless pointing devices become popular, it is critical that the button functions and positional status of a pointing device can be passed efficiently and correctly.
The cordless transducer/cursors in some of the prior arts have attempted to use frequency and/or phase changes to transmit the non-positional status of the transducer/cursor functions such as buttons pushed, pen pressure, or the like. However, if there is no sophisticated processing, frequency and phase changes are very prone to false reading resulting from several outside factors such as metal objects, noise, wireless electromagnetic wave and so on. These problems become more apparent, especially in a larger digitizer tablet.
Improvements have also been made in the prior arts to allow a user to use pointing devices on a digitizer tablet system in dual modes of operation that can provide information of either a relative movement or an absolute position under the control of the user.
However, this type of system has some disadvantages. One is that operating the pointing device in either a relative mode or an absolute mode is user-controlled but not automatically detected by the digitizer tablet system itself. Another disadvantage is that a position history table means is needed in order for the user to selectively control the use of the cursor device as an absolute position or as a relative movement device.
From the foregoing discussions, there is a need in the art for effectively and automatically detecting the pointing devices in a digitizer tablet system so that the digitizer tablet system may accommodate the dual operation modes by itself.